Image caption
The inaugural ball was a happier time for Mr Obama, whose wife's approval rating now eclipses his own

Barack Obama celebrates his 49th birthday on Wednesday. Grassroots organisers around the country are holding birthday events to help rally supporters, but will they help the president's flagging approval ratings?

In Washington DC, 18 months can seem like a lifetime. For President Obama, that frosty January morning when he took the oath of office before a veritable sea of well-wishers must seem like a distant memory.

Back then, over two-thirds of Americans rated him favourably. It seemed difficult to imagine that after 500 days in office, political pundits would be warning that this popular young president could be an albatross for vulnerable Democrats in November's mid-term elections.

And yet last week, Pennsylvania Senate candidate Joe Sestak, who is in a tough race against Republican Pat Toomey, told reporters he'd prefer that Michelle Obama campaign for him than her husband. She's now the most popular political figure in the country, according to a recent Gallup poll.

That scenario seemed unthinkable to the masses who lined Pennsylvania Avenue, huddling against the cold, to cheer the new president last January.

But in recent weeks, polling undertaken by the Gallup Organization has suggested disapproval of Mr Obama's presidency is outpacing approval on several occasions.

His approval rating, which has hovered around 47% for more than a month, hasn't broken 50% since mid-May.

Image caption
Both Hillary and Bill Clinton are now more popular than Mr Obama

His former rival Hillary Clinton has fared significantly better, achieving a 61% approval rating in 2010 - a figure matched by her husband, former President Bill Clinton.

Just 36% of Americans approve of Mr Obama's handling of the war in Afghanistan, down from 56% in July 2009, the poll suggests.

In mid July, a CNN/Opinion Research Corporation poll found support for Mr Obama's economic policies at a new low of 42%.

On another significant issue, the BP oil spill, a June poll conducted by CNN found 59% of survey respondents disapproved of Mr Obama's handling of the matter.

Slow change

As the chorus of critics grows, Mr Obama finds himself on the defensive. In two recent television interviews, the president was at pains to remind viewers that many of the problems he faced were handed to him when he took office.

But that's an argument the public seems increasingly immune to.

Presidential Approval Ratings

Figures for early August in the second year in office:

Barack Obama: 45%

George W Bush: 71%

Bill Clinton: 43%

George H W Bush: 74%

Ronald Reagan: 41%

Jimmy Carter: 39%

Gerald Ford: 48%

Richard Nixon: 55%

Source: Gallup

"Change has not come fast enough for too many Americans, I know that," Mr Obama admitted via video to the online activists and bloggers gathered at the liberal Netroots Nation convention.

That group were committed early supporters of Mr Obama, but have grown increasingly disgruntled with his presidency.

There seems nary a bright spot for Mr Obama.

But Jeff Jones, managing editor of the Gallup Poll, doesn't think this seemingly precipitous decline in support is particularly unusual.

"I think it is pretty normal, if you look at where other presidents stood at this point in their presidency," Mr Jones told the BBC.

Mr Obama's predecessor, President George W Bush, had impressively high ratings at this point in his presidency, driven largely by a spike in presidential support after the 9/11 attacks.

But Presidents Clinton, Reagan and Carter were all in the 40% range at a similar point in their presidencies. Indeed Mr Obama outperformed all three in July.

"The common thread with those presidents is that they all took office when the economy wasn't doing so well," Mr Jones said. "One difference is that Obama came into office more popular than most elected presidents, so maybe the expectations were a little bit higher."

But when the economy isn't doing well, it is nearly always the most pressing issue on voters' minds, and Mr Jones notes that it is very difficult for a president to have robust approval ratings with a weak economy.

"The economy is generally one of the stronger predictors of how people evaluate the president," he says, which doesn't bode well for Mr Obama's immediate political fortunes.

Still, the president's supporters are trying to capitalise on his 49th birthday today to reignite the energy and enthusiasm that characterised his campaign.

Campaign zeitgeist

After the election, the president's impressive campaign apparatus transformed into Organizing for America (OFA), a fundraising and activist organisation with access to the coveted e-mail and call lists compiled during Mr Obama's presidential campaign.

Image caption
The enthusiasm of the Obama campaign has dissipated during his presidency

OFA is eager to reactivate the millions of Americans who raised money, made phone calls and canvassed their neighbourhoods for Mr Obama.

OFA is attempting to use the president's birthday to provide both a boost for the commander-in-chief and encourage willing volunteers for Democrats in the mid-terms.

"The events that focus on anniversaries or that focus on the president as a personality or someone that people like and identify with tend to do well, so its understandable that they continue to try to tap that enthusiasm," Ari Melber, a writer for The Nation who has studied OFA, told the BBC.

"However, everyone knows there is significant concern from Obama's base about his progress on changing Washington."

OFA supporters received an e-mail from Michelle Obama, asking them to sign a birthday card for her husband, and "let him know that we're ready to take on the year ahead alongside him".

The Washington Post reports that, in what looks like a spot of campaign nostalgia, OFA is urging supporters to bust out their campaign '08 "yes we can" T-shirts, hats and buttons and wear them on Wednesday.

But while recapturing that campaign zeitgeist seems desirable, Mr Melber warns there are risks, particularly for some of the most active campaign supporters who have become some of the most disillusioned.

"There is always a risk that if you only do these kumbaya events and you don't give people meaningful voice then they may tune out," Mr Melber says.

"Most of these people would still like to see Mr Obama re-elected, so we are not talking about a real crisis in his political support. But walking around with a button or wishing the president a happy birthday doesn't really achieve anything either."

For Mr Obama, whose wife and daughters will be out of town for his birthday, it may not be such a happy birthday. Lucky for him, he still has one family member to celebrate with: Bo, the family dog.